Abstract
Deinococcus radiodurans is a Gram positive, non-sporing, red-pigmented tetracoccal bacterium, which is characterized by extreme resistance to irradiation. It was previously observed that survivors of γ-irradiated D. radiodurans wild-type strain IR cells could form, in addition to normal colonies, less-pigmented petite colonies (LPPC) on agar plate, and LPPC frequency was high (50 %). The LPPC morphology remained unchanged in sub-cultures (at least 10 times of transfer), suggesting that LPPC is a stable morphotype. Both of the morphology and LPPC frequency are special, so this LPPC phenomenon was further characterized in this study. Besides, we purpose the reason LPPC was formed, and solve the puzzle which the relation between LPPC effect and irradiation resistance. We found that UV, γ-ray and Mitomycin C were LPPC positive but not heating, and hydrogen peroxide, suggesting DNA damage dependence in LPPC. LPPC frequency was a function of UV radiation dose. Highest values obtained were around 30% of the survivors. However, we else isolated LPPC from survivors of γ-irradiated D. radiodurans radiation-sensitive mutant X2 cells. Purified LPPC clones from a batch of radiation treatment of D. radiodurans IR and its radiation-sensitive mutant X2 were similar found to be heterogeneous in cell volume as measured by a Coulter size analyzer. The highest values of cell volume were about 5 times that of the D. radiodurans IR that was around 8μm3. It also means that there is a large diversity in cell volume in the same specie. In this study, we isolated the cell volume mutants successfully, and our data shows LPPC effect was related with DNA damage, not irradiation resistance.